A power conversion device supplies power to a load by converting an AC voltage from an AC power supply into a DC voltage different from the AC voltage. When a circuit which converts the AC voltage of the AC power supply into the DC voltage makes the AC current flowing through the AC power supply have a sinusoidal waveform having the same phase as that of an AC power supply voltage, the best power factor is obtained and harmonic noise is also reduced. A circuit having an input current of a sinusoidal wave is called a power factor correction (PFC) circuit module.
The power conversion device detects a circuit current which flows from an AC power supply to a circuit to generate a control signal. There are various known methods for detecting the circuit current using a power conversion device.
(1) An inexpensive method is to insert a resistor with low resistance into a current path and detect a voltage which is generated on both ends thereof. However, this method requires a full-wave rectification circuit at a front stage. Accordingly, cost is reduced, but there is a problem that overall efficiency decreases due to the fact that full-wave rectification is needed.
(2) Another method is to use an insulation current transformer. In this case, there is a problem that cost increases due to the current transformer, but there is an advantage that high efficiency is achieved since the full-wave rectification is not required. These methods, however, cannot provide both high efficiency and inexpensive control.